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Correct the sky sub-object 0 live-byte figure; record the byte 7 anomaly

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The previous commit said "a mean of 6.99 of every 8 bytes are zero". That
is inverted. 6.99 is the mean count of live bytes, and the records are nearly
full rather than sparse. The live-byte histogram is 0:15, 2:1, 4:31, 5:238,
6:461, 7:1030, 8:1114.

That error also invalidated the reasoning built on it in this session's next
message, where the high zero-count was used to explain why the differential
analysis found no constant positions. There was no zero-density to explain.
The differential result stands -- all 8 positions vary -- but for the plain
reason that the records are dense, not because of any artifact.

New finding from re-examining it: byte 7 takes only 14 distinct values where
bytes 0-6 take 142-204. Its common values are 0x00 (1378), 0xff (806) and
0x80 (592), which are the high bytes of signed 16-bit values. That is
consistent with byte 7 being an MSB rather than ordinary data. Unexplained.

Also tried and recorded as not helping: a signed 16-bit reading spans
-32743..32633, near the full range, with no per-position structure (533, 371,
401 and 187 distinct at positions 0-3).
This commit is contained in:
ReaperOfVeriod
2026-10-11 03:52:40 +02:00
parent 3855169d48
commit 0ba790df1f
1 changed files with 12 additions and 5 deletions
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docs/formats/core-data-regions.md
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@@ -368,15 +368,22 @@ statistics below. The matched-control autocorrelation puts the peak at stride
**What it is made of:** **What it is made of:**
- **1,185 distinct `u32` values** across 5,780 words. - **1,185 distinct `u32` values** across 5,780 words.
- **Mean 6.99 of 8 bytes are zero**, so most records are sparse -- one or two - **Mean 6.99 of 8 bytes are live** -- the previous revision of this file said
live bytes in eight. "zero", which is inverted and wrong. The live-byte histogram is 0:15, 2:1,
4:31, 5:238, 6:461, 7:1030, 8:1114, so most records are nearly full rather
than sparse.
- **549 of 2,890 adjacent pairs (19%) are exact duplicates of each other.** The - **549 of 2,890 adjacent pairs (19%) are exact duplicates of each other.** The
most common 8-byte record, appearing 283 times, is `d7d7d780 d7d7d780` -- a most common 8-byte record, appearing 283 times, is `d7d7d780 d7d7d780` -- a
4-byte value stored twice. Others follow the same shape: `00051980 00051980`, 4-byte value stored twice. Others follow the same shape: `00051980 00051980`,
`00082580 00082580`. `00082580 00082580`.
**Not decoded.** Sparsity plus repeated entries is what a keyframe or index **Byte 7 is anomalous.** It takes only **14 distinct values** where bytes 0-6
table looks like, but nothing here establishes that, and the duplicated-4-byte take 142-204. Its common values are `0x00` (1378), `0xff` (806) and `0x80`
shape may equally be two adjacent records that happen to share a value. (592) -- the high bytes of signed 16-bit values, which is consistent with
byte 7 being an MSB of something rather than ordinary data. Unexplained.
**Not decoded.** A signed-16-bit reading was tried and does not obviously
help: the values span -32743..32633, close to the full range, with no
per-position structure (533, 371, 401 and 187 distinct at positions 0-3).
Recorded as a characterisation, with its range, so the next attempt starts Recorded as a characterisation, with its range, so the next attempt starts
from the composition rather than re-deriving it. from the composition rather than re-deriving it.